Infertility is a common health problem that affects 10-15% of couples of reproductive-age. According to the most recently released data, over 175,000 cycles of in vitro fertilization (IVF) were performed in 2012 in the United States alone (cdc.gov/art). This resulted in the culture of more than a million embryos annually with variable, and often ill-defined, potential for implantation and development to term. The live birth rate, per cycle, following IVF was just 29%, while on average 30% of live births resulted in multiple gestations (cdc.gov/art). Multiple gestations have well-documented adverse outcomes for both the mother and fetuses, such as miscarriage, pre-term birth, and low birth rate. Potential causes for failure of IVF are diverse; however, since the introduction of IVF in 1978, one of the major challenges has been to identify the embryos that are most suitable for transfer and most likely to result in term pregnancy.
Previous studies have demonstrated that more than half of human embryos are aneuploid, carrying an abnormal chromosome number, which contributes to the low efficiency of in vitro fertilization (IVF). Traditional methods of evaluating IVF embryos involve subjective assessment of static morphologic criteria. Although there is a relationship between static embryo morphology and ploidy, the correlation has been weak. Consequently, multiple embryos with variable implantation potential may be transferred, leading to both high rates of embryonic loss and increased frequency of multiple gestations with higher and well-documented maternal and perinatal risks.
In an effort to improve IVF success, clinics are increasingly using preimplantation genetic screening (PGS) in combination with growth to blastocyst stage to assist in selection of euploid embryos for transfer. Though invasive, the use of trophectoderm (TE) biopsy and 24-chromosome screening at the Day 5 blastocyst stage is associated with increased success in IVF. Other studies have failed to demonstrate a similar benefit with earlier Day 3 cleavage stage biopsy and fluorescent in-situ hybridization (FISH) assays of limited chromosome number and Day 3 biopsy with 24-chromosome screening is less common. PGS, however, involves additional patient cost, requires that the embryo be removed from its stable culture conditions to be subjected to invasive biopsy and remains illegal in certain countries.
Recent advances with non-invasive imaging have provided a non-invasive means to evaluate embryo viability, and to date reports indicate improved pregnancy rates in IVF clinics compared to standard morphologic embryo evaluation. Potential advantages of incorporating non-invasive imaging to the repertoire of tools available for embryo assessment include earlier embryo selection, thus diminishing the possible risks associated with prolonged culture, as well as avoiding the need for invasive embryo biopsy.
Previously, we and our collaborators used time-lapse imaging to demonstrate that human development to the blastocyst stage can be predicted by measuring cell cycle parameter timing prior to embryonic genome activation (EGA) by Day 2 of development. The parameters included the duration of the first cytokinesis, time between the two-cell and three-cell stage, and time between the three-cell and four-cell stage. We also recently demonstrated that precise cell cycle parameter timing windows are observed in euploid embryos to the four-cell stage, while four-cell aneuploid embryos exhibit diverse cell cycle parameter timing (20). However, whether these or other imaging parameters could be used to assess ploidy at later stages of embryonic development was uncertain.
Prior IVF methods of human embryo evaluation are thus lacking in several respects and can be improved by the present methods, which involve novel applications of time-lapse so microscopy, image analysis, and correlation of the imaging parameters with molecular profiles and chromosomal composition.